Personal computers have long incorporated the ability to produce sound by means of an audio device that converts digital signals controlled by the computer to analog audio waveforms. These analog signals may then be played through a speaker internal to the computer, or amplified and played through external speakers. The device that converts digital signals to analog audio output most often takes the form of an add-in adapter card, that contains both circuitry to interface the board to the computer system bus and circuitry to convert digital signals received from the computer to an analog audio waveform and amplify it.
Inclusion of Compact Disc players within computers later led to audio adapter cards that included the ability to route analog signals. When playing conventional audio CDS, the analog signal provided by the CD player within the computer is routed to the audio adapter in analog form, where it is routed to an amplifier at the control of the computer and played through the attached speakers. Alternatively, the compact disc player can provide a digital signal to the audio adapter, which then converts it to analog audio by means of a digital-to-analog converter before amplification. Most audio adapters currently available have the capability to play either a single digital audio signal provided over the computer bus or analog information provided by the internal compact disc player, but not both digital and analog information or digital information from two different sources.
The steady growth in multimedia capability of computers has brought about the ability to play CD audio, audio to accompany motion video or games, telephone or other communication audio, and system audio information such as traditional beeps. However, current products do not allow selection of more than one source for conversion to analog audio at the same time because a single digital-to-analog converter is present on an adapter for each channel of a stereo system. No provision is made for a configurable means of prioritizing audio sources for playing through the audio adapter.
This lack of ability to handle more than one audio signal at the same time in a configurable manner causes significant problems in computer systems incorporating several audio sources. Relatively unimportant system beeps may interrupt a movie being viewed by means of a DVD player, while important telecommunications audio such as notice of a phone call or fax may not be played at all. There is a need for a computer system to handle more than one audio source at the same time, in a manner that the user can configure based on his predetermined priorities.